Enterotoxigenic Escherichia coli with STh and STp genotypes is associated with diarrhea both in children in areas of endemicity and in travelers

Abstract

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea among children in developing countries and in travelers to areas of ETEC endemicity. ETEC strains isolated from humans may produce a heat-labile enterotoxin (LT) and two types of the heat-stable enterotoxin STa, called STh and STp, encoded by the estA gene. Two commonly used assay methods for the detection of STa, the infant mouse assay or different enzyme-linked immunosorbent assays, are unable to distinguish between the two subtypes of ST. Different genotypic methods, such as DNA probes or PCR assays, may, however, allow such discrimination. Using gene probes, it has recently been reported that ETEC strains producing STp as the only enterotoxin are not associated with diarrhea. In this study, we have used highly specific PCR methods, including newly designed primers for STh together with previously described STp primers, to compare the relative distribution of STh and STp in ETEC isolated from children with diarrhea in three different geographically distinct areas, i.e., Bangladesh, Egypt, and Guatemala, and from travelers to Mexico and Guatemala. It was found that ETEC strains producing STp were as commonly isolated from cases of diarrhea as strains producing STh both in Egypt and Guatemala, whereas STp strains were considerably less common in Bangladesh. No difference was found in the relative distribution of STh and STp in ETEC strains isolated from travelers with diarrhea and from asymptomatic carriers. Irrespective of ST genotype, the disease symptoms were also similar in both children and travelers.

FIG. 1.

STh and STp PCR of reference strains. The lane numbers are the same as the strain numbers in the table. Strains listed in the table were used in studies from references , , and . a, toxin profile was determined by gene probe assay by Steinsland et al. (17); all strains tested by the gene probes in Bergen, Norway, had been obtained from A.-M. Svennerholm's laboratory. b, strain was obtained as a reference strain collection from the WHO with ST genotypes indicated; the collection was originally prepared by Y. Takeda (21).

FIG. 2.

STp (A) and STh (B) PCR of ETEC strains from Guatemala. Lane Mw, molecular weight marker. Lanes 1 to 9, ETEC isolates; lane 10, STh- and STp-positive reference strain E17018/A; lanes 11 and 12, ETEC isolates; lane 13, PCR control without DNA; lane 14, ETEC isolate; lane 15, STp (in panel A)- and STh (in panel B)-positive reference strains.